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Projectiles and Newtons law help?

  1. Apr 9, 2015 #1
    The first question is about Newton's Third Law:
    A boat is moving north at a velocity v=15 km/h
    a man on the boat throws a ball horizontally with a velocity u=15 km/h
    how is the motion of the ball w.r.t the man?

    For this, I thought that because the boat is moving with the same speed as the ball, the ball should have no difference in speed, therefore it should be 0 m/s...but what confuses me is that the ball will have a parabolic motion because of the boats translation...so it should be less that 15 but not 0 m/s..Help?

    The second in on projectile motion
    3 cannons project the same mass at
    a) 45 degrees above the horizontal
    b) 0 degrees (on the horizontal)
    c) 45 degrees below the horizontal
    What are there final velocities?

    Should there final velocities be the same? regardless of angles? since all of the masses are affected by gravity g=9.81 m/s^2?

    Thank you!! :)
  2. jcsd
  3. Apr 9, 2015 #2


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    Hello FF, welcome to PF :smile: !

    Something went wrong with your posting: the template has disappeared. In this strange world of PF, its use is mandatory.
    Perhaps you want to read the guidelines that explain why.

    1. The problem statement, all variables and given/known data

    A clear and concise problem statement. The phrase "how is the motion of the ball w.r.t the man" is very unlikely quoted literally.

    2. Relevant equations

    You need something.

    3. The attempt at a solution
    Isn't just confusing for you. It's confusing for everybody.

    Try to order your thoughts and approach this as a math-like exercise, not some kind of poetry.. :smile:
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